Migrate custom extension example

Author: simolus3

sqlite3/example/custom_extension/example/main.dart

@@ -1,4 +1,4 @@
-import 'package:custom_extension/uuid.dart';
+import 'package:custom_extension/sqlite_vec.dart';
 import 'package:sqlite3/sqlite3.dart';
 
 void main() {

sqlite3/example/custom_extension/hook/build.dart

@@ -46,8 +46,8 @@ void main(List<String> args) {
 
         output.assets.code.add(
           CodeAsset(
-            package: 'custom_extension_native_assets',
-            name: 'uuid.dart',
+            package: 'custom_extension',
+            name: 'sqlite_vec.dart',
             file: targetFilePath,
             linkMode: DynamicLoadingBundled(),
           ),